The goal of this project is to develop a replicating recombinant vesicular stomatitis virus (rrVSV) that targets specifically to breast cancer cells and treats cancer by two mechanisms: 1) direct infection and killing of tumor cells and 2) stimulation of the immune system to recognize and kill breast cancer cells. Therapy for breast cancer is currently inadequate with approximately 40,000 women dying from metastatic disease each year. VSV is an efficient cell killer with a rapid replication rate. VSV is safe. It is endemic in certain human populations but is not pathogenic. We have created an rrVSV that preferentially infects breast cancer cells based on viral binding to the Her2/neu receptor. This rrVSV was highly effective in eliminating peritoneal implants of Her2/neu expressing tumor. Cured animals rejected rechallenge with Her2/neu expressing tumor and with parental tumors that did not express Her2/neu. Specific Aim 1 (SA1) will optimize the therapeutic efficacy of rrVSV. We will determine the maximum size tumor that can be eradicated, the optimal dose of virus, the effect of multiple viral administrations, the duration of viral persistence, the therapeutic effect of using a virus that expresses either GM-CSF or IL-12, the bystander effect on tumor cells that do not express Her2/neu and the toxicity of virus administration. SA2 will identify the immune cells that eradicate tumor following treatment with rrVSV. Successful therapy will be re-assessed in animals that are depleted in one of the following immune components: NK cells, macrophages, CD4 and/or CD-8 T-cells. SA3 will determine whether rrVSV treatment generates anti-tumor T-cells which find and eradicate tumors distant from the site of rrVSV therapy. SA4 will improve rrVSV by engineering mutations that enhance potency and specificity. This proposal uses new capabilities in constructing rrVSV to create an innovative, unique, flexible and theoretically sound treatment for a common, frequently incurable disease. The proposal focuses on breast cancer but could be equally applied to many other cancers for which suitable cell surface targets exist. [unreadable] [unreadable]